Fix Unpin impl of (Try)MaybeDone

Author: taiki-e

futures-util/src/future/maybe_done.rs

@@ -20,6 +20,8 @@ pub enum MaybeDone<Fut: Future> {
     Gone,
 }
 
+impl<Fut: Future + Unpin> Unpin for MaybeDone<Fut> {}
+
 /// Wraps a future into a `MaybeDone`
 ///
 /// # Examples

futures-util/src/future/try_maybe_done.rs

@@ -21,6 +21,8 @@ pub enum TryMaybeDone<Fut: TryFuture> {
     Gone,
 }
 
+impl<Fut: TryFuture + Unpin> Unpin for TryMaybeDone<Fut> {}
+
 /// Wraps a future into a `TryMaybeDone`
 pub fn try_maybe_done<Fut: TryFuture>(future: Fut) -> TryMaybeDone<Fut> {
     TryMaybeDone::Future(future)